1. Field of the Invention
This invention relates to programmable high pass filtering with automatic phase equalization for analog-to-digital conversion.
2. Description of the Related Art
Calculation of electrical signal energy consumed by an electrical load may be calculated as an integral over time, or as a sampling of values over time, of instantaneous power delivered or of the product of electrical current and voltage across the load. This calculated energy usually includes a contribution from the dc components in the circuit and a contribution of the remaining components. If one or more of the dc components is varying with time, a time varying error may arise in calculating the present value of energy consumed.
Other workers in this field have proposed various partial solutions for this problem. One such approach provides only ac coupling of the input signals--any dc coupling does not contribute to the computed value. A sensor employing ac coupling will cost more and will introduce phase shifts that will probably have to be (re)calibrated at regular time intervals. Further, inclusion of ac coupling will preclude use of this system by a user who wants or needs to sense dc signal values.
Other workers propose to dc couple the input signals, adding a high pass filter in one of the channels and compensating for phase with analog components. To improve the step response of the high pass filter and minimize settling time, poles of the filter(s) are placed as high in frequency as possible, consistent with avoidance of appreciable error in the magnitude response. This often introduces appreciable phase error at the desired signal frequencies, requiring additional phase error compensation with analog components. This compensation increases system cost and requires manual trimming of the analog components to specified values within the components' manufacturing tolerances.
What is needed is an array of high pass filters that can be inserted into, or removed from, the signal path(s) independently. Preferably, the system should provide greater user flexibility by allowing programmable use of high pass filters and should provide nearly perfect phase compensation of any phase error introduced by any high pass filter that is inserted. Preferably, this should be handled in the digital domain and should not require use of specially trimmed analog components.